This invention relates in general to apparatus and methods for testing earth formations, and more particularly to such apparatus and methods where a concurrent surface indication of an earth formation characteristic is provided during a drill stem test operation.
The method and apparatus of this invention is an improvement to the method and apparatus described in the following patents: U.S. Pat. No. 4,083,401, issued Apr. 11, 1978, E. Edward Rankin; U.S. Pat. No. 4,094,359, issued June 13, 1978, David W. King; and U.S. Pat. No. 4,108,243, issued Aug. 22, 1978, David W. King et al. In these patents, a method and apparatus for achieving concurrent surface indication of well characteristics is shown for drill stem testing and production tubing testing. In the drill stem testing operation, a packer is lowered in the well to a point a short distance above the formation to be tested. A bypass sub is mounted above the packer and connected to a drill string leading to the surface. The bypass sub has a bore that sealingly receives a wireline tool. A bypass passage extends around the bore to allow fluid to flow around the wireline tool while it is sealed in place.
In the operation, the wireline tool is lowered into the drill string and seated in the bore of the bypass sub. The bypass passage is selectively opened and closed by the wireline tool to allow fluid flow to the surface and also to allow a formation pressure buildup. The wireline tool has temperature and pressure gages which provide concurrent surface indication through the wireline to instruments located at the surface.
After the testing is completed, the wireline tool is withdrawn to the surface. Then a ball is pumped down the drill stem to a valve located above the bypass sub. The ball, under pressure, shears the valve to allow fluid from the well annulus to flow into the drill pipe. Pumps at the surface reverse circulate fluid from the well annulus up the drill pipe to remove the formation fluid from the drill pipe before removing the drill string.
While this method is satisfactory, in certain wells an unexpected amount of gas may be present. The gas will flow to the surface and through testing equipment where the flow rate and pressure is measured at the surface. The gas then must be flared off. A large quantity of gas may exceed the capabilities of the testing equipment, resulting in the burners being melted. The wireline instrument in the above mentioned patents does not have the capability of informing the operator that a large amount of gas is present in the formation.
Another disadvantage in the method taught in the above-mentioned patents is that the wireline tool must be completely withdrawn from the well before the well is killed by reverse circulating. At times, particularly if a large amount of gas or pressure is present in the drill stem, it would be preferable to kill the well before removing the wireline, since removing the wireline may take up to about an hour and must rely on pressure sealing equipment that seals against a moving wireline.